Glass is a highly durable and infinitely recyclable material, yet in practice only a small portion of architectural glass products re-enters the value chain after its first use. An increasing rate of energy retrofits of the EU building stock will result in replacement of 85% of existing windows in near future; in the current linear glass supply chain, this will generate large amounts of glass waste. Despite high recycling rates of container glass in Europe, window glazing is very rarely recycled into new glazing, and reuse is almost entirely unexplored. For aged glazing to be reused in construction, better knowledge of its surface quality and structural performance is needed. The main objective of this paper is to explore the effects of ageing and exposure to indoor and outdoor environment on the strength of glass. A comparative investigation is undertaken to evaluate the strength and surface quality of the internally, externally and cavity-facing glass surfaces of insulating glass units (IGUs) after 30 years of use in a building envelope in the Netherlands. The glass panes are separated from the IGU assembly and cut into specimens for microscopy and coaxial double ring tests. The study shows that the visual quality is best preserved on the cavity-facing surface, consequently exhibiting the highest bending strength. The internally and externally facing surfaces, with visibly more extensive damage, exhibited similarly lower strengths at low probabilities of failure. When compared to the design strength of new annealed glass acc. to EN 16612, all the surfaces showed a reuse potential, with considerable bending strength.@en

This article presents the metric avoided carbon for the reuse of aluminium unitised curtain wall façades, that are to be taken from a donor building an applied onto a receiving building. The metric is used to compare seven proposed circular reuse strategies, each showing a different level of reuse. Based on literature and reference studies, we identify those parts of the façade where reuse has the most impact and is technically feasible. The seven reuse strategies and the avoided carbon method are applied on a real case study building as donor project and a fictitious building as receiving project. We conclude that reuse is technically feasible, saves carbon, and that the proposed metric can help to incentivize building owners and project developers to adopt circular reuse.@en

In the evolution of structural glass beam elements, the requirements for post-fracture load bearing capacity and safe failure behaviour have led to the development of reinforced and post-tensioned beams. Maximum bending capacity in the post-fracture state is normally associated with extensive yielding of the reinforcement, providing a safe failure mechanism through apparent ductility of the composite beam section. This can be achieved as long as the propagation of primary flexural cracks does not compromise the transfer of shear from the load points to the supports. Although shear failure is typically not critical for the ultimate limit state design of ’normal’ unreinforced glass beams, it may govern the load-bearing and deformation capacity in the post-fracture state for reinforced and post-tensioned glass beams. This paper presents exploratory experiments and initial analysis of the shear failure phenomenon in the post-fracture state of reinforced and post-tensioned glass beams. Potential shear transfer mechanisms are identified based on the critical shear crack theory developed for reinforced concrete members and applied in the analysis of shear failures observed in four-point bending tests of post-tensioned glass beams. The behaviour of fractured laminated glass under mixed-mode (tension+shear) loading is explored on a limited set of small-scale double-notched glass specimens, demonstrating the feasibility of the applied test methodology. Preliminary findings of the present study may serve as a basis for further investigations of shear resistance of glass beams. Typical shear failure kinematics and suitable constitutive laws of the applied materials need further investigation in order to provide design recommendations for the prediction of shear resistance of reinforced and post-tensioned glass beams.

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The effectiveness of post-tensioning in enhancing the fracture resistance of glass beams depends on the level of compressive pre-stress introduced at the glass edge surface that will in service be exposed to tensile stresses induced by bending. Maximum pre-load that can be applied in a post-tensioned glass beam system, yielding maximum compressive pre-stress, is limited by various failure mechanisms which might occur during post-tensioning. In this paper, failure mechanisms are identified for a post-tensioned glass beam system with a flat stainless steel tendon adhesively bonded at the bottom glass edge, including the rupture of the tendon, glass failure in tension and adhesive/glass failure in the load introduction zone. Special attention is given to the load introduction failure given that the transparent nature of glass limits the use of vertical confinement usually applied in concrete. An analytical model for determination of the allowable pre-load in post-tensioned glass beams is proposed, based on the model applied for externally post-tensioned concrete beams. The model is verified with the results of a numerical model, showing good correlation, and applied in a parametric study to determine the influence of various beam parameters on the effectiveness of post-tensioning glass beams.

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The concept of post-tensioned glass beams builds on the concrete analogy of the reinforced glass beams. By additionally prestressing the reinforcement in a post-tensioned system, a compressive pre-stress is applied on the glass, enhancing the initial fracture resistance in bending. This paper presents three post-tensioned beam systems tested in four-point bending. The effects of both adhesive bonding and mechanical anchoring of tendons are explored in order to define an optimised beam system which can provide a significant level of compressive pre-stress and maximise the efficient use of material. The tests demonstrate the feasibility of post-tensioning by providing a substantial level of additional load capacity and redundancy to commonly applied laminated glass beams. Several specimens have demonstrated premature failure governed by lateral-torsional buckling or by shear. Since glass beams are generally not strengthened through transversal reinforcement, as concrete elements, further investigation of the mechanism of shear failure is particularly important. Analytical models, based on the pre-stressed concrete theory, provide expressions for determination of the initial fracture resistance, initial stiffness and ultimate flexural capacity. Compared with the experimental results, the models provide close prediction values for the initial fracture loads, while the predictions of the initial stiffness and ultimate post-fracture load capacity show less consistency. Closer prediction requires a better understanding of the effect of specific anchoring, the level of composite action and the post-fracture behaviour of laminated glass (including long-term and temperature effects).

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This paper presents a study on post-tensioned glass beams in a statically indeterminate system. In order to increase the safety of structural glass beams, ductile reinforcement can be added to glass beam sections providing secondary load carrying mechanism in case of glass breakage. In the here investigated post-tensioned system, the reinforcement tendons are additionally pre-tensioned, introducing compressive pre-stress in the beam in order to increase the apparent tensile strength of glass. The system is tested in five-point bending at 23°C and 60°C in order to investigate the basic structural performance and the influence of temperature increase on the initial cracking load and the behaviour of the cracked beam. The benefit of the here investigated statically indeterminate system is a more economical design, i.e. lowering of the bending moment in the span of an equivalent simply supported system by continuing the beam over the central support. The efficiency of the applied system is compared to a reinforced beam system produced in the same batch with similar overall dimensions. The results show an increase of initial cracking load of the post-tensioned beams due to the applied pre-stress and a ductile post-cracking response, reaching high ultimate loads prior to failure. At 60°C both reinforced and post-tensioned beams show lower initial cracking loads and limited post-cracking ductility but still significant load reserve with ultimate loads well above the initial cracking loads, providing safe failure behaviour.@en